Call spec.loader.exec_module in _load_pybind11_module utility

[traversaro]

I am not 100% sure about this change, but without this change the torchcodec build of conda-forge fails after the upgrade from pybind11 2.* to pybind11 3.* during tests with error like:

 │ =========================== short test summary info ============================
 │ FAILED test/test_decoders.py::TestDecoder::test_create[file_like_rawio-VideoDecoder-asset0] - AttributeError: module 'core_pybind_ops' has no attribute 'create_from_file_like'
 │ FAILED test/test_decoders.py::TestDecoder::test_create[file_like_rawio-AudioDecoder-asset1] - AttributeError: module 'core_pybind_ops' has no attribute 'create_from_file_like'
 │ FAILED test/test_decoders.py::TestDecoder::test_create[file_like_rawio-AudioDecoder-asset2] - AttributeError: module 'core_pybind_ops' has no attribute 'create_from_file_like'
 │ FAILED test/test_decoders.py::TestDecoder::test_create[file_like_bufferedio-VideoDecoder-asset0] - AttributeError: module 'core_pybind_ops' has no attribute 'create_from_file_like'
 │ FAILED test/test_decoders.py::TestDecoder::test_create[file_like_bufferedio-AudioDecoder-asset1] - AttributeError: module 'core_pybind_ops' has no attribute 'create_from_file_like'
 │ FAILED test/test_decoders.py::TestDecoder::test_create[file_like_bufferedio-AudioDecoder-asset2] - AttributeError: module 'core_pybind_ops' has no attribute 'create_from_file_like'
 │ FAILED test/test_decoders.py::TestDecoder::test_create[file_like_custom-VideoDecoder-asset0] - AttributeError: module 'core_pybind_ops' has no attribute 'create_from_file_like'
 │ FAILED test/test_decoders.py::TestDecoder::test_create[file_like_custom-AudioDecoder-asset1] - AttributeError: module 'core_pybind_ops' has no attribute 'create_from_file_like'
 │ FAILED test/test_decoders.py::TestDecoder::test_create[file_like_custom-AudioDecoder-asset2] - AttributeError: module 'core_pybind_ops' has no attribute 'create_from_file_like'
 │ FAILED test/test_ops.py::TestVideoDecoderOps::test_create_decoder[file_like_rawio-cpu] - AttributeError: module 'core_pybind_ops' has no attribute 'create_from_file_like'
 │ FAILED test/test_ops.py::TestVideoDecoderOps::test_create_decoder[file_like_bufferedio-cpu] - AttributeError: module 'core_pybind_ops' has no attribute 'create_from_file_like'
 │ FAILED test/test_ops.py::TestAudioDecoderOps::test_file_like_decoding[cpu-0] - AttributeError: module 'core_pybind_ops' has no attribute 'create_from_file_like'
 │ FAILED test/test_ops.py::TestAudioDecoderOps::test_file_like_decoding[cpu-1024] - AttributeError: module 'core_pybind_ops' has no attribute 'create_from_file_like'
 │ FAILED test/test_ops.py::TestAudioDecoderOps::test_file_like_method_check_fails - AttributeError: module 'core_pybind_ops' has no attribute 'create_from_file_like'
 │ FAILED test/test_ops.py::TestAudioDecoderOps::test_file_like_read_fails - AttributeError: module 'core_pybind_ops' has no attribute 'create_from_file_like'
 │ FAILED test/test_ops.py::TestAudioDecoderOps::test_file_like_read_less_than_requested[half] - AttributeError: module 'core_pybind_ops' has no attribute 'create_from_file_like'
 │ FAILED test/test_ops.py::TestAudioDecoderOps::test_file_like_read_less_than_requested[minus_10] - AttributeError: module 'core_pybind_ops' has no attribute 'create_from_file_like'
 │ ============ 17 failed, 702 passed, 98 skipped in 109.81s (0:01:49) ============

to be honest, I do not know enough about Python module loading to understand why this happens in conda-forge CI, and not in torchcodec CI that also uses pybind11 3.* . However, the problem goes away if after loading the module, we also execute spec.loader.exec_module . Looking around it seems that this may be related to multi-phase init (for example pybind/pybind11#5574), but to be honest I do not know enough about that to understand if that is the case.

[traversaro]

Sorry for the branch noise, I did not realized that GitHub started creating branch inside torchcodec itself, my bad!